This invention relates to flame resistant compositions. More particularly, this invention relates to flame resistant polymer compositions. Even more particularly, this invention relates to flame resistant polymers with a synergistic mixture of flame retardant and compatible additive which allows a lower concentration of flame retardant to be used than would otherwise be effective. The invention further provides a method for rendering polymers flame resistant.
Many polymer compositions are not ordinarily flame resistant. In fact, certain polymers, such as polyolefins, can be highly flammable. Imparting flame resistance to polymer compositions can be highly desirable or even required for polymers to be useful in certain applications such as those in the textile field. Various compounds are known to impart flame resistance to polymer compositions.
The use of sterically hindered amines to render polymers flame resistant is well known. Hindered amines have been previously added to polyolefins to impart resistance to the effects of light, heat and oxygen. Certain hindered amines, however, were previously found to be incompatible with some flame retardants and other compounds. Specifically, organohalogenated and organosulfur compounds were found to interfere with the activity of some hindered amines as photostabilizers. A subset of these hindered amines, however, are compatible with such compounds. These hindered amines are known as N-alkoxy (or NOR) substituted hindered amines or NOR hindered amine light stabilizers (NOR HALS). U.S. Pat. No. 5,096,950, for example, discloses the use of NOR substituted hindered amines in conjunction with a polyolefin substrate. Similarly, U.S. Pat. No. 5,393,812 discloses the use of a halogenated hydrocarbyl phosphate and phosphonate ester flame retardant with an alkoxyamine hindered amine to render a polyolefin product flame retardant, light stable, and resistant to fading. It was subsequently determined that N-alkoxy substituted hindered amines function as not only light stabilizers, but also impart flame resistance to polyolefins.
The discovery of the utility of NOR substituted hindered amines as flame retardants provided several benefits including the elimination of certain toxic compounds from flame resistant articles. For example, some halo-organic compounds generate toxic by-products both during production and in the case of combustion of the final product. Additionally, some metal-containing flame retardants such as antimony oxides sometimes contain trace amounts of arsenic compounds.
The use of NOR substituted hindered amines as flame retardants and their structure are well known and are described in PCT Application PCT/US98/13469 (WO99/00450). One useful NOR substituted hindered amine is sold under the tradename CGL-116.
The use of NOR substituted hindered amines as flame retardants generally involves blending the NOR substituted hindered amine with a polymer and, optionally, additional components, followed by melt compounding the mixture into pellets. The polymer can then be processed into fiber, for example, by extruding. While the concentrations at which certain NOR substituted hindered amines are effective as flame retardants are generally lower than those at which brominated flame retardants are effective, it is still desirable to minimize the amount of these compounds used in order to minimize cost. For example, the cost of NOR substituted hindered amines represent a major portion of the cost of producing flame resistant fabrics.
It is also generally desirable to insure that any flame retardant compound used is homogeneously dispersed in the polymer to maximize its effectiveness and insure that excess flame retardant is not required to insure effective incorporation of the flame retardant in all portions of the polymer article. This is particularly important when using flame retardants that do not easily incorporate uniformly into a resin during extrusion.
It is further desirable to be able to add pigments to polymer compositions that do not interfere with the activity of the flame retardant, yielding colored flame retardant compositions. This is particularly desirable in industries such as the automotive fabric industry where colored flame resistant fabrics are currently produced by combining flame resistant fibers and non-flame resistant fibers. When both flame resistant and non-flame resistant fibers are combined in a non-woven fabric, concerns exist over non-homogeneous blending of the two types of fibers. If the blending is not homogeneous, localized areas of the fabric may not have sufficient concentration of flame resistant fibers for the complete article to be flame resistant.
It is, therefore, an object of the present invention to provide a flame resistant composition comprising a polymer and a synergistic mixture comprising a non-halogenated flame retardant compound and a compatible additive.
It is another object of the present invention to provide a flame resistant composition wherein a flame retardant compound is homogeneously dispersed through a polymer.
It is still another object of the present invention to provide a flame resistant composition comprising a polymer and a synergistic mixture comprising a non-halogenated N-alkoxy hindered amine and carbon black.
It is yet another object of the present invention to provide a flame retardant compound comprising a non-halogenated flame retardant compound and a pigment that does not interfere with the flame retardant compound.
It is still another object of the present invention to provide a method of rendering a polymer flame resistant comprising compounding a polymer with a synergistic mixture comprising a non-halogenated flame retardant compound and a compatible additive.
It is yet another object of the present invention to provide a method of rendering a polymer flame resistant comprising dispersing a non-halogenated N-alkoxy hindered amine homogeneously through a polymer.
It is still another object of the present invention to provide a method of rendering a polymer flame resistant comprising compounding a polymer with an effective amount of a synergistic mixture comprising a non-halogenated N-alkoxy hindered amine and carbon black.
It is yet another object of the present invention to provide a method of rendering a polymer flame resistant comprising dispersing a non-halogenated flame retardant compound and a pigment that does not interfere with the flame retardant compound.
It is still another object of the present invention to provide a flame resistant fiber comprising a polymer and a synergistic mixture comprising a non-halogenated flame retardant compound and a compatible additive.
It is still another object of the present invention to provide a pigmented flame resistant fiber comprising a polymer, a non-halogenated flame retardant compound, and a pigment that does not interfere with the flame retardant compound.
It is still another object of the present invention to provide a flame resistant fabric comprising a polymer and a synergistic mixture comprising a non-halogenated flame retardant compound and a compatible additive.
It is yet another object of the present invention to provide a pigmented flame resistant fabric comprising a polymer, a non-halogenated flame retardant compound, and a pigment which does not interfere with the flame retardant compound.
At least one or more of the foregoing objects, together with the advantages thereof over the known art relating to the use of flame retardants in polymer compositions, which shall become apparent from the specification which follows, are accomplished by the invention as hereinafter described and claimed.
In general the present invention provides a flame resistant composition comprising(a) a polymer; (b) a synergistic mixture comprising (i) from about 0.6 to about 3 percent of a non-halogenated flame retardant compound; and (ii) at least about 0.06 percent of a compatible additive; wherein said percentages are based on weight percent of (a) plus (b), wherein (a) plus (b) equals 100 percent.
The present invention also includes a method of rendering a polymer flame resistant comprising compounding said polymer with a synergistic mixture comprising (i) from about 0.6 to about 3 percent of a non-halogenated flame retardant compound; and (ii) at least about 0.06 percent of a compatible additive; wherein the percentages are based on weight percent of polymer plus the synergistic mixture, and wherein polymer plus synergistic mixture equals 100 percent.
These and other objects and advantages are obtained by the composition of the present invention, the general nature of which may be stated as compounding a polymer with a mixture of a compatible additive and a NOR substituted hindered amine flame retardant. The compatible additive aids in evenly distributing the flame retardant throughout the polymer. Without such a compatible additive, the flame retardant is not as easily incorporated uniformly into the polymer. For example, when a polymer such as polypropylene is extruded with the NOR substituted hindered amine CGL-116, an elevated temperature (compared to that required for the extrusion polypropylene without CGL-116) is required in the entry zones of the extruder to enable thorough mixing of the polymer and the flame retardant. We have also noted that extrusion of CGL-116 and polypropylene requires an extrusion apparatus design that enables greater mixing in the extruder than is otherwise required when CGL-116 is not present.
When the compatible additive is carbon black, it acts as a compatible additive and as a pigment. Lower levels of carbon black yield a gray polymer composition while higher levels of carbon black render the composition black.
It had been previously believed that the addition of carbon black as a pigment would require an increased amount of flame retardant in order to maintain flame resistance of the polymer. This belief was based on the rationale that carbon black would absorb the flame retardant and render it unavailable to act as a flame retardant. Surprisingly, it was discovered that addition of carbon black did not necessitate an increase in the level of CGL-116 required to maintain flame resistance, but instead, decreased it. While not wishing to condition patentability on any particular theory of action, we believe that the carbon black acts as a dispersing agent which adsorbs the flame retardant and is more easily dispersed into the polymer than the flame retardant alone. This belief is supported by the observation that when polypropylene is extruded with CGL-116, fewer filament breaks and godet wraps are observed when carbon black is present than when it is absent. Additionally, filaments appear to be more visually uniform when carbon black is a component of the extrudate.
The present invention is directed toward a flame resistant composition comprising a synergistic mixture of a flame retardant and a compatible additive. The present invention is also directed toward a method for imparting flame resistance to a polymer composition using a synergistic mixture of a flame retardant and a compatible additive.
Preferred flame retardants are NOR substituted hindered amines, which have the formula 
where G1 and G2 are independently alkyl of 1 to 4 carbon atoms or are together pentamethylene, Z1 and Z2 are each methyl or Z1 and Z2 together form a linking moiety which may additionally be substituted by an ester, ether, amide, amino, carboxy or urethane group, and E is C1-C18 alkoxy, C5-C12 cycloalkoxy, C7-C25 aralkoxy, or C6-C12 aryloxy. NOR substituted hindered amines are commercially available. For example, the Ciba-Geigy Corporation of Tarrytown, N.Y. markets NOR substituted hindered amines under the tradenames Tinuvin 123 and CGL-116.
A preferred NOR substituted hindered amine is the melt process able amine CGL-116. The major component of this formulation has the formula 
where the R group is 
A preferred compatible additive is carbon black. At sufficient concentrations, carbon black also functions as a pigment that does not interfere with the functioning of the flame retardant. Other preferred compatible additives include pigments formed by mixing several basic pigments, e.g., red, yellow, white and the like, with carbon black. These pigment mixtures can function as colorants at sufficient concentrations so long as none of the non-carbon black pigments interfere with the functioning of the flame-retardant. It is also preferred to precompound the flame retardant and the compatible additive prior to compounding these materials with a polymer. This is believed to insure maximum interaction between the compatible additive and the flame retardant prior to compounding with the polymer, thus insuring maximum homogeneous dispersion of the flame retardant through the polymer.
Optionally, supplemental components may also be added to the flame resistant composition. These include conventional additives such as halo-organic or metal-containing flame retardants, antioxidants, UV absorbers and light stabilizers, pigments, metal deactivators, phosphites and phosphonites, peroxide destroying compounds, polyamide stabilizers, basic co-stabilizers, hydroxylamine co-stabilizers, nucleating agents, fillers, reinforcing agents, plasticizers, lubricants, emulsifiers, optical brighteners, insecticides, fungicides, bactericides, antistatic agents, and extrusion aids.
The polymers of the present invention are preferably homopolymers or copolymers of an alpha-olefin. Preferred homopolymers include polyethylene, polypropylene, polybutylene, and mixtures thereof. Preferred copolymers include ethylene/propylene copolymers, polypropylene-butene-1 copolymers, polypropylene/octene-1 copolymers, ethylene/butene-1 copolymers, ethylene/octene-1 copolymers and acrylonitrile/butadiene/styrene (ABS). Polypropylene is an especially preferred polymer.
The composition of the present invention may take any form including that of fibers, yarns, fabrics or textiles, films, sheets, or coatings. Textiles include all types of fabric, including woven, non-woven, knitted, and tufted fabrics. Preferred forms include fibers and fabrics made from the fibers. Non-woven fabrics are especially preferred. It is envisioned that conventional equipment and techniques can be used to prepare the composition of the present invention. It should be understood that the term xe2x80x9cfibersxe2x80x9d includes cut and uncut fibers and filaments and continuous filaments.
The present invention is also directed toward a flame resistant composition comprising a polymer with improved homogeneous distribution of flame retardant NOR substituted hindered amines throughout the polymer. This improved distribution of the flame retardant is established by the use of a compatible additive in the extrusion of the flame resistant composition. The use of a compatible additive in this manner allows for greater economy in the manufacture of flame resistant polymer compositions due to the decreased amount of flame retardant required and due to a greater ease of manufacture as evidenced by the occurrence of fewer breaks and godet wraps during extrusion. The use of a compatible additive also provides for a higher uniformity and therefore, higher quality, of the final product.
The present invention is also directed toward a method for rendering a polymer flame resistant. This method comprises mixing a polymer with the synergistic mixture of the present invention. A preferred method of mixing the polymer and the mixture is by extrusion. It is also preferred that the flame retardant and the compatible additive be premixed together prior to mixing these materials with a polymer.